System and method for laser based internal analysis of gases in a body of a human

ABSTRACT

A device, system and method for measuring free gas in a cavity of a subject. The device, system and method include a light source for emitting light with a wavelength associated with an absorption band of the free gas, an optical fibre connected to the light source and adapted to be inserted using an introducing member for internal illumination, and a detector adapted to be positioned on a skin surface for detecting light transmitted through the tissue. The device, system and method further includes a control unit for evaluating the detected transmitted light for determining the free gas, or a distribution of the free gas, or concentration of the free gas.

This application is a National § 371 stage of PCT International PatentApplication No. PCT/EP2016/069549, filed Aug. 17, 2016, which claimsforeign priority benefit of Swedish Patent Application No. SE 1500335-3,filed Aug. 17, 2015, the disclosures of each of which patentapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

This disclosure pertains to analysis of gases in a body of a human, bypositioning a light source, such as a fibre connected to a laser, insidea cavity of the body. Especially, the disclosure relates to positioningthe light source in the trachea, or in the digestive system, such as inthe oesophagus or the intestines, for performing measurements onphysiological gases.

Description of the Prior Art

Physiological gases, such as, oxygen, nitrogen, nitric oxide (NO),carbon dioxide, and water vapour exist inside many cavities in the humanbody, for example, lungs, sinuses, and the middle ear. The digestivesystem is a further location for gases. Oxygen in the lungs is ofspecial interest as it is a prerequisite for vital functions of a human.Monitoring oxygen in the lungs is of interest, particularly, forpremature new-born infants. In connection with the diseases in thecavities of the head, for example, sinusitis or otitis media, the gasfilled cavity may be filled with liquids and the gas signal willdecrease or disappear.

Substances may be identified with optical spectroscopy by utilizingcharacteristic absorption signals. While the spectroscopic signals fromliquids and solids are relatively broad, typically 10's of nanometers,free gases are characterized by absorption lines being about 10000 timessharper, typically around 0.001 nm. This difference in the absorptionsignal makes it possible to detect free gases in cavities or poresenclosed by condensed material, such as human tissue. This is thefundamental principle for the technology called GASMAS (Gas inScattering Media Absorption Spectroscopy) technology, S. Svanberg, Gasin Scattering Media Absorption Spectroscopy—from Basic Studies toBiomedical Applications, Lasers and Photonics Reviews 7, 779 (2013).

The GASMAS technology has been used for characterizing sinuses andmiddle ear, for example in S. Svanberg, L. Persson and K. Svanberg,Human cavity gas measurement method and device; Swedish PatentApplication 0500878-4; L. Persson, M. Andersson, M. Cassel-Engquist, K.Svanberg and S. Svanberg, Gas Monitoring in Human Sinuses using TunableDiode Laser Spectroscopy, J. Biomed. Optics 12, 2028 (2007); L. Persson,M. Lewander, M. Andersson, K. Svanberg and S. Svanberg, SimultaneousDetection of Molecular Oxygen and Water Vapor in the Tissue OpticalWindow using Tunable Diode Laser Spectroscopy, Applied Optics 47, 2028(2008); M. Lewander, Z. G. Guan, K. Svanberg, S. Svanberg and T.Svensson, Clinical System for Non-invasive in situ Monitoring of Gasesin the Human Paranasal Sinuses, Optics Express 13, 10849 (2009); M.Lewander, S. Lindberg, T. Svensson, R. Siemund, K. Svanberg, S.Svanberg, Clinical Study Assessing Information on the Maxillary andFrontal Sinuses using Diode Laser Gas Spectroscopy, Rhinology 50, 26(2011); J. Huang, H. Zhang, T. Q. Li, H. Y. Lin, K. Svanberg, and S.Svanberg, Assessment of Human Sinus Cavity Air Volume using TunableDiode Laser Spectroscopy, with Application to Sinusitis Diagnostics, J.Biophotonic DOI 10.1002/jbio.201500110; K. Svanberg and S. Svanberg,Monitoring of Free Gas In-Situ for Medical Diagnostics using LaserSpectroscopic Techniques, in Frontiers in Biophotonics for TranslationalMedicine, U.S. Dimish and M. Olivo (eds) (Springer, Singapore 2015)307-321; H. Zhang, J. Huang, T. Q. Li, S. Svanberg, and K. Svanberg,Optical Detection of Middle Ear Infection using SpectroscopicTechniques—Phantom Experiments, J. Biomedical Optics 20, 057001 (2015).The GASMAS technology has also been used in studies for characterizationof gases in lungs and intestines in full-term newborn infants, P.Lundin, E. Krite Svanberg, L. Cocola, M. Lewander Xu, G. Somesfalean, S.Andersson-Engels, J. Jahr, V. Fellman, K. Svanberg, and S. Svanberg,Non-invasive Monitoring of Gas in the Lungs and Intestines of NewbornInfants using Diode Lasers: Feasibility Study, J. Biomedical Optics 18,127005 (2013); E. Krite Svanberg, P. Lundin, M. Larsson, J. Akeson, K.Svanberg, S. Svanberg, S. Andersson-Engels and V. Fellman, Non-invasivemonitoring of oxygen in the lungs of Newborn Infants Using Diode LaserSpectroscopy, Pediatrics Research, 79, 621 (2015).

Both oxygen and water vapour may be registered in most of the cases, butnot always. The reason a signal was not detected may be due to the lowsignal strength after the detected light had passed a long path throughthe enclosing tissue.

Hence, new improved apparatus and methods for detecting free gasesinside cavities of the human body are advantageous.

SUMMARY OF THE DISCLOSURE

Accordingly, embodiments of the present disclosure preferably seek tomitigate, alleviate or eliminate one or more deficiencies, disadvantagesor issues in the art, such as the above-identified, singly or in anycombination by providing a device, system or method according to thedescription for measuring free gas in a cavity, such as a lung or in thedigestive system.

In accordance to a first aspect, a device for measuring free gas in acavity of a subject is disclosed. The device comprises a light sourcefor emitting light with a wavelength associated with an absorption bandof the free gas; an optical fibre connected to the light source andadapted to be inserted internally in the subject using an introducingmember; a detector unit adapted to be positioned on a skin surface fordetecting light transmitted through tissue of the subject. The devicefurther comprises a control unit for evaluating the detected transmittedlight for determining a concentration of the free gas or a distributionof the free gas.

In some examples of the disclosure, the control unit of the device maybe configured for detecting the free gas in the cavity.

In some examples of the disclosure, the light source of the device maybe a laser.

In some examples of the disclosure, the device may comprise at least twolight sources having different wavelengths.

Additionally, in some examples of the disclosure, at least one lightsource of the at least two light sources may have a wavelengthassociated with an absorption band of a reference gas.

In some examples of the disclosure the reference gas may be watervapour.

In some examples of the disclosure may the free gas be a physiologicalgas or a mixture of gases.

In some examples of the disclosure the physiological gas may be any ofoxygen, nitric oxide (NO), carbon dioxide, and water vapour.

In some examples of the disclosure the optical fibre may include a lightdiffusor at an end of the optical fibre adapted to be position in anintroducing member.

In some examples of the disclosure the control unit may be configuredfor controlling a medical ventilator based on the distribution of thefree gas, or the concentration of the free gas.

In some examples of the disclosure the control unit may be configuredfor controlling an administration of a medicament based the distributionof the free gas, or the concentration of the free gas.

In some examples of the disclosure the control unit may be configuredfor activating an alarm when the determined the free gas, or thedistribution of the free gas, or the concentration of the free gasreaches or passes a selected threshold value.

In some examples of the disclosure the distribution of the free gas, orthe concentration of the free gas may be used for determining a lungfunctioning of the subject.

In some examples of the disclosure the light may be emitted from morethan one location, and the transmitted light may be detected by morethan one detector unit.

In some examples of the disclosure diffuse optical tomography may beused for evaluating the distribution of the free gas.

In some examples of the disclosure the evaluation may be obtained as athree-dimensional gas distribution.

In some examples of the disclosure the detector unit may be an imagingsensor configured, and the light source sequentially emitting anabsorbing wavelength and a close non-absorbing wavelength, and the imagesensor detecting two images which may then be compared by the controlunit.

In some examples of the disclosure the control unit may evaluate lineprofile changes in an absorption spectrum for determining theconcentration of the free gas or the distribution of the free gas.

In a further aspect, a system for measuring free gas in a cavity of asubject is disclosed. The system comprises an introducing member to bearranged in a channel or duct of the subject; a light source foremitting light with a wavelength associated with an absorption band ofthe free gas; an optical fibre connected to the light source and adaptedto be inserted into the introducing member; and a detector unit adaptedto be positioned on a skin surface for detecting light transmittedthrough tissue of the subject. The system may further include a controlunit for evaluating the detected transmitted light for determining theconcentration of the free gas or the distribution of the free gas.

In some examples of the disclosure the introducing member may be either:a tracheal tube, an endotracheal tube, a bronchoscope, an endoscope, ora colonoscope.

In some examples of the disclosure the introducing member may be anasogastric feeding tube adapted to be inserted into the oesophagus.

In some examples of the disclosure the introducing member may have anexpandable balloon or cuff.

In some examples of the disclosure the expandable balloon of cuff may bemade from a light diffusing material.

In some examples of the disclosure the inner walls of the expandableballoon of cuff may have a light reflecting coating.

In some examples of the disclosure the expandable balloon of cuff may bearranged at an end section of the introducing member.

In some examples of the disclosure an end section of the introducingmember may be coupled to the optical fibre.

In some examples of the disclosure the optical fibre may be embeddedinto a wall of the introducing member.

In a further aspect, a method of measuring free gas in a cavity of asubject is disclosed. The method comprising the steps of arranging anintroducing member in a channel of the subject;

-   -   positioning an optical fibre connected to a light source in        introducing member;    -   positioning a detector unit on a skin surface;    -   emitting light using the light source, the emitted light having        a wavelength associated with an absorption band of the free gas;    -   detecting light transmitted through the tissue by the detector        unit; and    -   evaluating the detected transmitted light using a control unit        for determining the concentration of the free gas or a        distribution of the free gas.

In some examples of the disclosure may the detector at positioned at thechest of the subject.

In some examples of the disclosure the channel may be a trachea or anoesophagus.

In some examples of the disclosure the detector may be positioned at theabdomen of the subject.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of which examples ofthe disclosure are capable of will be apparent and elucidated from thefollowing description of examples of the present disclosure, referencebeing made to the accompanying drawings, in which:

FIG. 1 is illustrating an example of a disclosed device and system;

FIGS. 2A, 2B, 2C and 2D are illustrating examples of arrangements of alight source in the trachea for measuring lung functions;

FIG. 3 is illustrating a further example of an arrangement of a lightsource using a bronchoscope for measuring lung functions; and

FIGS. 4A and 4B are illustrating further examples of an arrangementwherein a light source is inserted through the oesophagus.

DESCRIPTION OF EXAMPLES

Specific examples of the disclosure will now be described with referenceto the accompanying drawings. This disclosure may, however, be embodiedin many different forms and should not be construed as limited to theexamples set forth herein; rather, these examples are provided so thatthis disclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art.

The following disclosure focuses on examples of the present disclosureapplicable to analyse or monitoring free physiological gases in humancavities by arranging a light source in a cavity, such as in thetrachea, or in the digestive system, such as in the oesophagus or theintestines, such as parts of the digestive tract and detecting thetransmitted light using one or a plurality of detectors arranged outsidethe human body.

For example, this is advantageous for detecting weak signals due to thelight passing a long path through the tissue enclosing the cavity.

When monitoring gases using narrow-band light, such as laser light, thelight has been transmitted towards the skin over the cavity containingthe free gas, such as the lungs or intestines. The light that haspenetrated enough tissue to reach the cavity is scattered andtransmitted to a detector positioned against the skin a few centimetreslaterally the light source. Thereby is a non-invasive measurementprocedure performed but the light transmitted from the light source thatreaches the detector will be heavily attenuated by the tissue the lighthas to pass between the light source and the detector and the scatteredlight will then be further attenuated when transmitted back through thetissue to the detector. As an example, if a portion of around 0.001 ofthe light transmitted towards the skin reaches the cavity comprising thefree gases, another attenuation factor of 0.001 has to be applied to thelight travelling back from the cavity to be detected by the detectorarranged on the surface of the skin. Hence the observed light whichreaches the detector is about a millionth of the light transmitted bythe light source towards the skin.

In the disclosed examples, the light source is arranged to transmitlight to the tissue with losses as low as possible and then detect thelight at the surface of the skin. By arranging the light sourceinternally for decreasing the attenuation factor of the lighttransmitted to the tissue for measuring the free gas in a cavity, thetotal attenuation factor may be reduced to about 0.001 which is about1000 times larger than what was previously be achieved.

The disclosed devices, systems and methods utilize a member forintroducing the light sources for injecting the light into the tissue,for example, a bronchoscope, a nasogastric feeding tube, endoscope, atracheal tube, a colonoscope or similar introducing members.

The group of patients considered to be most relevant when it comes toapplying GASMAS technology for monitoring free gases in cavities arepremature new-born infants. These infants often experience respiratorycomplications, such as breathing difficulties and problems with the lungfunctioning. Premature new-borns are therefore often connected to amedical ventilator to assist them with moving air into and out of thelungs. When connected to a medical ventilator, a premature new-borninfant is intubated by a tracheal tube, such as an endotracheal tube. Inone example of the description it is described how a fibre opticalarrangement for delivering light to a cavity, such as the lung, may beconducted in combination with a tracheal tube, such as an endotrachealtube while detection of transmitted light is made at the skin surface.

In another example of the description it is described how a fibreoptical arrangement for delivering light to a cavity, such as the lung,may be conducted in combination with a nasogastric feeding tube insertedinto the oesophagus while detection of transmitted light is made at theskin surface.

Additionally, in another example, the light from the optical fibrearrangement is distributed over a larger distance or area by a lightdiffusing material.

Additionally, and/or alternatively, the transmitted light is detected atthe skin surface by one or a plurality of detectors positioned at theskin over the cavity such as the lung. The detectors may be configuredto be arranged at the skin surface or other means, such as opticalfibres, could be used to collect the light at the skin surface anddirect the collected light to a detector. In one example, a plurality ofdetectors may be used in parallel or sequentially to detect gases or adistribution of gases, or gas concentrations in different parts of thebronchial tree of a patient.

In this way, the results of changes in the settings of the medicalventilator or medications may be directly observed, and the informationfrom the observation may be used to optimize the treatment of thepatient using a feed-back system.

In some examples, the detection is made frequency- andphase-sensitively. The light, such as laser light, from the light sourcemay be wavelength modulated at a selected frequency, and synchronousintensity variations may be detected when the modulation is conductedaround a gas absorption wavelength. When modulation is conducted closeto a gas absorption wavelength, the intensity of the detected light willquickly change at small variations of the wavelength, as described in S.Svanberg, Gas in Scattering Media Absorption Spectroscopy—from BasicStudies to Biomedical Applications, Lasers and Photonics Reviews 7, 779(2013), which is incorporated herein by reference.

Alternatively, in some examples, a skin area may be detected by animaging sensor, such as a digital camera, with high intensity dynamicboth at an absorbing wavelength and at a close non-absorbing wavelength.The two images may then be compared, for example by division orsubtraction, whereby the areas affected by gases may be visualized.

The same technology as described above for cavities, such as lungs, maybe applied to monitoring gases, gas distribution or gas concentration inother cavities, for example in the digestive system, such as in theintestines. Here the light may be injected using an optical fibrearrangement in combination with a channel in an endoscope, an endoscopefor esophagogastroduodenoscopy, or colonoscope or other minimallyinvasive devices. Abnormal gas distribution in the intestines, such asparts of the digestive tract, may be seen, for example when diagnosingthe serious illness, necrotizing enterocolitis (NEC).

When utilizing the GASMAS technology, the determination of a gasconcentration may be affected by the path length in the tissue the lightinteracting with the gas in the cavity has to travel through. The pathlength in the tissue is unknown due to multiple scattering. Hence lighttravelling both longer and shorted distances through the tissue may bedetected at the same time. Beer-Lambert's relation which is normallyused when analysing gas gives that the intensity of the absorptionsignal is determined by the product of the gas concentration and thepath length (see S. Svanberg, Atomic and Molecular Spectroscopy—BasicAspects and Practical Applications, 4th Edition, Springer, Berlin,Heidelberg 2004, which is incorporated herein by reference). When thepath length is known, which is the case when measuring in anon-scattering material, the gas concentration may be directlycalculated.

When utilizing the GASMAS technology for measuring a gas concentration,the path length through the gas is unknown; this need to be accountedfor when performing a gas concentration measurement. Different methodmay be used for handling the problems of an unknown path length, theseare discussed in, for example L. Mei, G. Somesfalean and S. Svanberg,Pathlength Determination for Gas in Scattering Media AbsorptionSpectroscopy, Sensors 14, 3871 (2014), which is incorporated herein byreference.

One of the most exact methods is to use profile changes in an absorptionspectrum of, for example a water vapour absorption line. The changes inthe profile of the water vapour line are dependent on the oxygenconcentration, see P. Lundin, L. Mei, S. Andersson-Engels and S.Svanberg, Laser Spectroscopic Gas Concentration Measurements inSituations with Unknown Optical Path Length Enabled by Absorption LineShape Analysis, Appl. Phys. Lett. 103, 034105 (2013), which isincorporated herein by reference. This method requires a good signal tonoise ratio since the influence of the oxygen on the water vapour lineis weak.

Another option is to perform the GASMAS measurements both for the gasconcentration to be determined and for water vapour. The water vapourconcentration may be assumed to be saturated in tissue and wherein theconcentration is determined by the temperature which is known, see A. L.Buck, Buck Research Manuals; Updated Equation from (1981), which isincorporated herein by reference. New Equation for Computing VaporPressure and Enhancement Factor. J. Appl. Meteorol. 20, 1527 (1996),which is incorporated herein by reference. Based on the measured watervapour signal the effective path length may be calculated. The obtainedpath length may be approximately the same as for the gas, such asoxygen, nitric oxide (NO), or carbon dioxide, with an unknownconcentration to be determined. The gas concentration, such as foroxygen, nitric oxide (NO), and carbon dioxide, may then be directlycalculated using the approximated path length. This method works bestwhen the light absorption and the light scattering in the tissue is thesame for both measurements which is the case when the wavelengths usedfor the measurements are close. For example, oxygen is normallymonitored around some of the sharp components in the oxygen molecule'sA-band about 760 nm. Water vapour has a strong absorption around, forexample 935 nm, but the difference in wavelength compared to oxygen mayneed to be corrected for due to differences in the optical properties atthe different wavelengths. Therefore the weaker absorption wavelengthfor water vapour at around 820 nm may be a better choice.

One example of an implementation is illustrated in FIG. 1 . The patient1 in this example is a premature new-born baby. The new-born baby isconnected to a medical ventilator 2 due to, under the circumstancescommon disorder, Respiratory distress syndrome (RDS).

The medical ventilator 2 is connected to the intubated patient 1 via,for example, an endotracheal tube 3 inserted in the trachea 4. In thisexample, two light sources 5, 6 are used for measuring a gas, forexample oxygen at about 760 nm, and water vapour at about 820 nm.Depending on the measured gas other wavelengths may be used. In someexamples other gases than water vapour may be used as a reference gas.The requirement is only that the gas concentration may be calculatedwithout using the path length the detected light has travelled.

Alternatively, in other examples only one light source may be used. Insome other examples more than two light sources may be used fordetecting further gases, gas distributions or gas concentrations.

Alternatively other configurations of the light sources may be possiblewhen using other methods related to GASMAS as previously describedherein.

The light sources may be semiconductor lasers, for example distributedfeed-back lasers (DFBL), vertical cavity surface emitting lasers (VCSEL)or other types of available lasers. The effect of the emitted light ispreferably in the range 1 to 3000 mW.

The lasers may be driven by a current and temperature regulating unitincluded in the drive unit 7. The drive unit 7 may be controlled by acontrol unit 8, such as a computer. The control unit 8 may be used forsignal processing and evaluation of the measured data.

Additionally, in some examples, the control unit 8 may be connected tothe controller 9 of the medical ventilator 2 for controlling thesettings of the medical ventilator 2. Additionally and/or alternatively,the controller 9 may also be used to control the distribution ofmedicaments 10 to the patient 1.

Additionally, in some examples, the lasers may be wavelength modulatedby modulating the drive current on two separate frequencies. Thefrequencies may typically be in the region around 10 kHz to allow noisereduced phase-sensitive detection (lock-in-detection).

By using separated modulation frequencies, different gases, such asoxygen, nitric oxide (NO), and carbon dioxide, and water vapour, may beseparated even though the light injection may be carried out through thesame fibre 11. Light from individual optical fibres 12 connected to thelight sources, such as the semiconductor lasers 5, 6, may be connectedto a single injection fibre 11.

Additionally, in some examples, a small portion of the light to beinjected may be diverted optically, such as by a fibre, to a calibrationunit 13. The calibration unit 13 may be a gas cell including a gas to bedetected, such as oxygen, nitric oxide (NO), and carbon dioxide. The gashas a known concentration and the gas cell has a predetermined length.The calibration unit 13 may also include a droplet of water and atemperature measuring unit. All parts of the calibration unit 13 mayhave a common detector unit.

Alternatively, in some examples, a compact diffuse multi-pass cell madefrom a porous material, such as ceramic may be used. The porous materialmay be enclosed in a compact gas cell, see T. Svensson, E. Adolfsson, M.Lewander, C. T. Xu and S. Svanberg, Disordered, Strongly ScatteringPorous Materials as Miniature Multi-pass Gas Cells, Phys. Rev. Lett.107, 143901 (2011), which is incorporated herein by reference.

The main part of the individually frequency marked light is led throughoptical fibre 11 down through the, in this example used, endotrachealtube 3.

In the example illustrated in FIG. 2B to 2D the fibre 11 ends with adiffusor. The diffusor may be a structure on the surface of the fibre ora separate part made from a light scattering material. The diffusor isused to have the light distributed over a larger surface to reach adecreased surface power. A lower surface power may help to avoid raisein temperature of the tissue. Another advantage is eye safety if testsare performed outside the human body.

In some examples the injected light transmitted from the end of the endof the optical fibre 11, such as through the diffusor, may betransmitted to the tissue without passing any air in the trachea. If thelight passes through air, the air may give some background signal inlight detected by the detectors 14.

In one example, an inflatable cuff or balloon made from opticallyscattering material and with reflecting material on the inner walls maybe used to have as much light as possible to be directly transmittedinto the tissue, as seen in FIG. 2A.

The example illustrated in FIG. 2A gives good positioning of the opticalfibre for monitoring the upper part of the lungs. By using abronchoscope and a diffusing fibre end the light injection may be madedeeper into the bronchial tree as illustrated in FIG. 3 .

Alternatively and/or additionally, in some examples more than one, suchas at least two, positions are used for light injection. When using morethan one location for measuring, the measurements for the differentlocations need to be performed sequentially. Alternatively, more thanone controllable standard fibre may be used.

When using more than one location for light injection and to obtain abetter three-dimensional gas distribution analysis, diffuse lighttomography may be used, as described in the articles J. Swartling, J.Axelsson, S. Svanberg, S. Andersson-Engels, K. Svanberg, G. Ahlgren, K.M. Kalkner and S. Nilsson, System for Interstitial Photodynamic Therapywith On-line Dosimetry—First Clinical Experiences of Prostate Cancer, J.Biomed. Optics 15, 058003 (2010), which is incorporated herein byreference; and T. Durduran, R. Choe, W. B. Baker and A. G. Yodh, DiffuseOptics for Tissue Monitoring and Tomography, Rep. Progr. Phys. 73,076701 (2010), which is incorporated herein by reference.

The detector or detectors 14 is/are adapted to be arranged against theskin. The detector should have a surface sized to detect the lighttransmitted through the tissue, for example in the range 0.25 to 5 cm²,such as 1 cm². The detector may be made from different materials, suchas germanium.

The detected light is transmitted as an electrical signal to the controlunit 8. The signal may be evaluated using digital lock-in technologysequentially or in parallel, as described in the article L. Mei, and S.Svanberg, Wavelength Modulation Spectroscopy—Digital detection of GasAbsorption Harmonics based on Fourier Analysis, Applied Optics 54, 2254(2015), which is incorporated herein by reference.

Alternatively, in some examples an analogue lock-in-amplifier may beused. The analogue lock-in-amplifier may be connected to the controlunit 8.

Additionally, in some example threshold values may be selected. When themeasured value has reached or passed the selected threshold values analarm 15 may be activated for the health care personnel. The alarm 15may be an acoustic alarm or an electronic alarm to a surveillancecenter.

FIGS. 2 A to 2D are illustrating different examples of how to utilize atracheal tube, such as an endotracheal tube.

FIG. 3 is illustrating an example wherein diffused light is injectedusing a working channel of a bronchoscope.

It may be observed that the same equipment, with some modification, maybe used for external injection of light into the human body in thosecases wherein a medical ventilator with a tracheal tube, or abronchoscope is not used, for example through a feeding tube through theoesophagus. In these cases the light may be expanded and made diffusedby a scattering medium with a large enough surface, for example a fewcm², made in contact with the skin. This arrangement makes it possibleto avoid local increase in tissue temperature, and eye safety isachieved.

FIG. 1 is illustrating an exemplary configuration of the discloseddevice and system. Patient 1 is connected to a medical ventilator 2 viaan introducing member 3, such as a bronchoscope, a tracheal tube, or anendotracheal tube, connected to the trachea 4.

In some other examples the introducing member 3 may be, for example, anasogastric feeding tube. The light sources 5, 6, such as lasers, withwavelength associated to the free gas of interest, for example, oxygen,nitric oxide (NO), and carbon dioxide, and a reference gas, for examplewater vapour.

In some examples other gases than water vapour may be used as areference gas. The requirement is only that the gas concentration may becalculated without using the path length the detected light hastravelled.

Alternatively, in other examples only one light source may be used. Insome other examples more than two light sources may be used fordetecting further gases, gas distributions or gas concentrations.

Alternatively other configurations of the light sources may be possiblewhen using other methods related to GASMAS as previously describedherein.

The light sources are connected to the drive unit 7, which is controlledby the control unit 8.

In some examples the measured value of the free gas in the lungs may beused for affecting the controller 9 for controlling the setting of themedical ventilator 2. Alternatively and/or additionally, in someexamples, the measured value by the control unit 8 may be used toadministration of a medicament 10.

The light it emitted to the tissue via an optical fibre 11. Light fromindividual optical fibres 12 connected to the light sources 5, 6, suchas the semiconductor lasers, may be connected to a single fibre 11.

Additionally, in some examples, a small portion of the light to beinjected may be diverted optically, such as by a fibre, to a calibrationunit 13.

A detector 14 is configured to be positioned at a skin location at thechest of the patient for detecting the transmitted diffused light. Thedetected light carries information about the gas concentration in thelungs or gas distribution in the lung tissue, such as oxygen, nitricoxide (NO), and carbon dioxide concentration or distribution.

Additionally, in some examples, an alarm 15 may be activated when themeasured value reaches or passes a selected threshold value.

FIGS. 2A to 2D are illustrating different examples of coupling the lightform the optical fibre to the tissue for measuring lung functioning.

FIG. 2A is illustrating an example of a trachea tube 3, such as anendotracheal tube, with a balloon or cuff 16 being inflatable to preventair leakage next to the trachea tube 3 which includes the optical fibre11 for transmitting light down the trachea.

FIG. 2B is illustrating an example of an optical fibre 11 brought down atrachea tube, such as an endotracheal tube, to its end. At the end alight diffusor 17 is arranged as an ending to the optical fibre 11.

FIG. 2C is illustrating an example of how light in the fibre 11 may beconnected to the end section 18 of a trachea tube, such as anendotracheal tube. The end section is made from a non-absorbing butstrongly light scattering material.

FIG. 2D is illustrating an example of light from an optical fibre 11 maybe coupled to a balloon or cuff 16. The balloon or cuff may be made froma non-absorbing but light scattering material. In some examples, theinner walls are coated 19 with a light reflecting material.

In an example, the laser light source is applied via the oesophagusrather than the trachea. In this example, the laser light source may becombined with the nasogastric feeding tube that is used in most infantsin neonatal intensive care. The use of the nasogastric feeding tube forlight application is advantageous because most infants already need tohave such a device inserted, so no additional device needs to beintroduced for the majority of patients. It is also advantageous sincethe oesophagus environment is less sensitive to infection, so thesterility requirements for the device could potentially be relaxed. Itis also advantageous due to that the oesophagus is normally mostlycollapsed, so there is potentially not a need for an expanding cuff tocreate good optical contact between the light source and the tissue.Further, lower parts of the lungs may also be more easily reached.

The light source should be positioned at a point in the oesophagus thatrepresents a position close to the lungs. In an example, an opticalfibre that guides the laser light is combined with the nasogastricfeeding tube, so that the optical fibre goes along the tube to anadequate position along the tube. Nasogastric feeding tubes have marksthat indicate how deep the tube is inserted, and these marks can be usedto determine the position of the light source in the oesophagus.

In a preferred example, the optical fibre that guides the laser light isembedded in the tube wall during manufacturing of the nasogastricfeeding tube, so that the nasogastric feeding tube and laser light guidecomes as a single device.

In an example, the distal end of the optical fibre is terminated with alight diffusor that distributes the light over a larger area than wouldbe provided by the fibre tip only. In a preferred example, when theoptical fibre is embedded in the tube wall as described above, thediffusor is implemented by designing the tube wall in front of the fibretip with light scattering properties so that the light scatters over anarea along the tube corresponding to the desired characteristics of thediffusor. In an alternative example, the diffusor is manufactured as aseparate component that is embedded in the tube wall similarly to theoptical fibre.

In an example, alternatively, the diffusor can be made part of anexpandable cuff similar to the diffusor described in connection with thetrachea herein above.

The optical fibre may also be positioned in the nasogastric tube in sucha way, that it may be sequentially moved to different positions alongthe tube for facilitating, e.g. a full tomographic view of the gasdistribution, such as oxygen, nitric oxide (NO), and carbon dioxidedistribution, using multiple detectors 14.

Alternatively, a plurality of optical fibres may be used in parallel atdifferent positions for facilitating, e.g. a full tomographic view ofthe gas distribution, such as oxygen, nitric oxide (NO), and carbondioxide distribution, using multiple detectors 14.

In alternative examples, the light source on the nasogastric feedingtube is implemented by placing one or multiple laser diodes directly atthe site where the light source should be, and having electrical wiresfor driving the laser diodes along the nasogastric feeding tube. Thisimplementation may also be applied to the cases of a tracheal tube.

FIG. 4A illustrates an optical fibre 41 combined with a nasogastricfeeding tube 46 inserted into the oesophagus 42. The relation with thetrachea 43 and the lungs 44 is also shown. At the distal end of theoptical fibre 41, there may be a light diffusor 45. The upper part ofthe stomach 47 is also shown.

FIG. 4B illustrates a close-up of the optical fibre 41, embedded intothe tube wall of the nasogastric feeding tube 46. The nasogastricfeeding tube is inserted in the oesophagus 42. In this example, theoptical fibre has a diffusor 45 at the distal end of the optical fibre41. In other examples the optical fibre 41 may not have a diffusor.

The same examples of implementations described in relation tointroducing the optical fibre for measuring free gases in a cavity usingthe trachea and the oesophagus are also applicable when using, forexample, an endoscope or a colonoscope for evaluating abnormal gasdistributions or gas concentrations in the intestines, or the digestivetract. In these cases the detector may be adapted to be positioned onthe abdomen of the subject.

The present invention has been described above with reference tospecific examples. However, other examples than the above described areequally possible within the scope of the disclosure. Different methodsteps than those described above, performing the method by hardware orsoftware, may be provided within the scope of the invention. Thedifferent features and steps of the invention may be combined in othercombinations than those described.

The indefinite articles “a” and “an,” as used herein, unless clearlyindicated to the contrary, should be understood to mean “at least one.”The phrase “and/or,” as used herein, should be understood to mean“either or both” of the elements so conjoined, i.e., elements that areconjunctively present in some cases and disjunctively present in othercases.

The invention claimed is:
 1. A system for measuring free gas in lungs ofa subject based on spectroscopy, the system comprising: an introducingmember being a nasogastric feeding tube adapted to be inserted into anoesophagus of the subject; a light source for emitting light at anabsorbing wavelength of the free gas; an optical fiber connectable tothe light source is embedded into a wall of the introducing member andthe introducing member is configured for positioning a light emittingend of said fiber near to bronchi while the introducing member extendsinto a stomach of the subject; a plurality of detector units adapted tobe positioned on a skin surface, at a chest of the subject, fordetecting light at the skin surface which has been transmitted from thelight emitting end through tissue and the skin surface of the subject;and a control unit for evaluating the detected transmitted light fordetermining the free gas in the lungs, or a distribution of the free gasin the lungs, or a concentration of the free gas in the lungs, such thatthe free gas, the distribution of the free gas or the concentration ofthe free gas is determinable for each lung by the control unit based onan evaluation of the detected transmitted light.
 2. The system of claim1, wherein the introducing member has an expandable balloon or cuff. 3.The system of claim 2, wherein the expandable balloon or cuff is (i)made from a light diffusing material and/or (ii) arranged at an endsection of the introducing member, and/or the inner walls of theexpandable balloon or cuff has a light reflecting coating.
 4. The systemof claim 1, wherein an end section of the introducing member is adaptedto be coupled to the optical fiber.
 5. The system of claim 1, whereinthe light source comprising at least two light sources having differentwavelengths.
 6. The system of claim 5, wherein at least one light sourcehas a wavelength associated with an absorption band of a reference gas.7. The system of claim 6, wherein the reference gas is water vapour. 8.The system of claim 1, wherein the free gas is a physiological gas or amixture of gases.
 9. The system of claim 8, wherein the physiologicalgas is at least one selected from oxygen, nitric oxide, carbon dioxide,and water vapour.
 10. The system of claim 1, wherein the control unit isconfigured for controlling a medical ventilator based on thedistribution of the free gas, or the concentration of the free gas. 11.The system of claim 1, wherein the control unit is configured foractivating an alarm when determined that the free gas, or thedistribution of the free gas, or the concentration of the free gasreaches or passes a selected threshold value.
 12. The system of claim 1,wherein the distribution of the free gas, or the concentration of thefree gas, is used for determining lung functioning of the subject.
 13. Amethod of measuring free gas in lungs of a subject, the methodcomprising: arranging an introducing member being a nasogastric feedingtube into an oesophagus of the subject; wherein an optical fiberconnected to a light source is embedded into a wall of the introducingmember; positioning the introducing member so that a light emitting endof the optical fiber is near or adjacent to bronchi of the subject whilethe introducing member is extending into a stomach of the subject,positioning a plurality of detector unit on a skin surface of a chest ofthe subject; emitting light using the light source, wherein the emittedlight has a wavelength associated with an absorption band of the freegas; detecting light transmitted from the light emitting end through thetissue and the skin surface of the subject by the plurality of detectorunits; and determining free gas in the lungs, a distribution of the freegas in the lungs, or a concentration of the free gas in the lungs byevaluating the detected transmitted light using a control unit fordetermining the free gas, or a distribution of the free gas, or aconcentration of the free gas in each lung.